Inkjet recording methods can easily form images at low costs, and thus are employed in various printing fields. As an inkjet ink, known is an ink containing photocurable compounds, which cure through polymerization and crosslinking upon irradiation with actinic radiation (hereinafter also simply referred to as “actinic radiation-curable ink”). Such actinic radiation-curable inks have drawn attention in recent years since images with high adhesion can be formed even on recording media showing low water absorption.
Examples of the photocurable compounds include radically polymerizable compounds which cure through polymerization using radicals as reaction centers, and cationic polymerizable compounds which cure through polymerization using cations as reaction centers. When actinic radiation-curable inks contain photocurable compounds, polymerization initiators are known to be contained in inks so as to initiate polymerization more efficiently. As examples of the polymerization initiators, known are radical polymerization initiators that can generate radicals upon irradiation with actinic radiation, and cationic polymerization initiators that can generate cations upon irradiation with actinic radiation.
Also known is a technique in which gelling agents are contained in actinic radiation-curable inks such that the inks undergo sol-gel phase transition reversibly through a temperature change. Such inks, when the temperature of the inks lowers upon impact on recording media, undergo gelation due to crystallization of the gelling agents. Accordingly, pinning properties of the inks upon impact on recording media are enhanced and thus coalescence of adjacent dots is less likely to occur, and consequently higher-definition images can be formed (see, Patent Literature (hereinafter, abbreviated as PTL) 1 and PTL 2, for example).